PCT application WO90/09800, published Sep. 7, 1990, and incorporated herein by reference, describes various modifications of reproductive hormones. In addition, this publication discloses that protein pharmaceuticals and hormones in general may be modified to extend their biological half-lives in vivo by ligation of the carboxy terminal portion of the HCG-.beta. subunit or a variant thereof to the carboxy terminus. The PCT application disclosure does not specifically address tandem extensions with multiple carboxy terminal portions (CTP) of the HCG-.beta. chain. The present invention is directed to such tandem extensions.
Human chorionic gonadotropin (HCG) is one of at least four reproductive hormones in a family which also includes follicle stimulating hormone, luteinizing hormone, and thyroid stimulating hormone. All of these hormones are comprised of .alpha. subunits which are identical among the group, and .beta. subunits which differ according to the member of the family. The .beta. subunit of HCG is substantially larger than that of the remaining three hormones in that it contains approximately 34 additional amino acids at the C-terminus referred to herein as the carboxy terminal portion (CTP) which is considered responsible for the comparatively longer serum half-life of hCG as compared to other gonadotropins (Matzuk, M. et al., Endocrinol (1989) 126:376). In the native hormone, this CTP extension contains four mucin-like O-linked oligosaccharides.